Facebook has also sold stakes to Microsoft and a handful of venture capital funds. The company, which makes money from online advertising, is trying to ride out the recession -- just like the rest of us.

Digital Sky has funded Internet companies in Russia and Eastern Europe, including social networking sites that reach 350 million people.

Zuckerberg, who recently marked his 25th birthday. He was worth an estimated $1.5 billion in 2008 and is the youngest person to appear in the Forbes 400 richest Americans.

But he may have dropped below billionaire status in the last year, and the estimated value of his company dropped from the $15 billion it was worth when Microsoft bought a 1.6% stake for $240 million.